53 research outputs found
Integrated optics for astronomical interferometry. I. Concept and astronomical applications
We propose a new instrumental concept for long-baseline optical single-mode
interferometry using integrated optics which were developed for
telecommunication. Visible and infrared multi-aperture interferometry requires
many optical functions (spatial filtering, beam combination, photometric
calibration, polarization control) to detect astronomical signals at very high
angular resolution. Since the 80's, integrated optics on planar substrate have
become available for telecommunication applications with multiple optical
functions like power dividing, coupling, multiplexing, etc. We present the
concept of an optical / infrared interferometric instrument based on this new
technology. The main advantage is to provide an interferometric combination
unit on a single optical chip. Integrated optics are compact, provide
stability, low sensitivity to external constrains like temperature, pressure or
mechanical stresses, no optical alignment except for coupling, simplicity and
intrinsic polarization control. The integrated optics devices are inexpensive
compared to devices that have the same functionalities in bulk optics. We think
integrated optics will fundamentally change single-mode interferometry.
Integrated optics devices are in particular well-suited for interferometric
combination of numerous beams to achieve aperture synthesis imaging or for
space-based interferometers where stability and a minimum of optical alignments
are wished.Comment: 11 pages, 8 figures, accpeted by Astronomy and Astrophysics
Supplement Serie
The interferometric baselines and GRAVITY astrometric error budget
GRAVITY is a new generation beam combination instrument for the VLTI. Its
goal is to achieve microarsecond astrometric accuracy between objects separated
by a few arcsec. This accuracy on astrometric measurements is the most
important challenge of the instrument, and careful error budget have been
paramount during the technical design of the instrument. In this poster, we
will focus on baselines induced errors, which is part of a larger error budget.Comment: SPIE Meeting 2014 -- Montrea
High spatial resolution monitoring of the activity of BA supergiant winds
There are currently two optical interferometry recombiners that can provide
spectral resolutions better than 10000, AMBER/VLTI operating in the H-K bands,
and VEGA/CHARA, recently commissioned, operating in the visible. These
instruments are well suited to study the wind activity of the brightest AB
supergiants in our vicinity, in lines such as H or BrGamma. We present
here the first observations of this kind, performed on Rigel (B8Ia) and Deneb
(A2Ia). Rigel was monitored by AMBER in two campaigns, in 2006-2007 and
2009-2010, and observed in 2009 by VEGA; whereas Deneb was monitored in
2008-2009 by VEGA. The extension of the Halpha and BrGamma line forming regions
were accurately measured and compared with CMFGEN models of both stars.
Moreover, clear signs of activity were observed in the differential visibility
and phases. These pioneer observations are still limited, but show the path for
a better understanding of the spatial structure and temporal evolution of
localized ejections using optical interferometry.Comment: Proceedings of conf. IAUS272 - Active OB stars - Paris, July 19-23,
201
Characterization of integrated optics components for the second generation of VLTI instruments
Two of the three instruments proposed to ESO for the second generation
instrumentation of the VLTI would use integrated optics for beam combination.
Several design are studied, including co-axial and multi-axial recombination.
An extensive quantity of combiners are therefore under test in our
laboratories. We will present the various components, and the method used to
validate and compare the different combiners. Finally, we will discuss the
performances and their implication for both VSI and Gravity VLTI instruments.Comment: SPIE Astronomical Instrumentation 2008 in Marseille, France --
Equation (7) update
Integrated optics for astronomical interferometry - VI. Coupling the light of the VLTI in K band
Our objective is to prove that integrated optics (IO) is not only a good
concept for astronomical interferometry but also a working technique with high
performance. We used the commissioning data obtained with the dedicated K-band
integrated optics two-telescope beam combiner which now replaces the fiber
coupler MONA in the VLTI/VINCI instrument. We characterize the behaviour of
this IO device and compare its properties to other single mode beam combiner
like the previously used MONA fiber coupler. The IO combiner provides a high
optical throughput, a contrast of 89% with a night-to-night stability of a few
percent. Even if a dispersive phase is present, we show that it does not bias
the measured Fourier visibility estimate. An upper limit of 0.005 for the
cross-talk between linear polarization states has been measured. We take
advantage of the intrinsic contrast stability to test a new astronomical
prodecure for calibrating diameters of simple stars by simultaneously fitting
the instrumental contrast and the apparent stellar diameters. This method
reaches an accuracy with diameter errors of the order of previous ones but
without the need of an already known calibrator. These results are an important
step of integrated optics and paves the road to incoming imaging interferometer
projects
Characterizing closure-phase measurements at IOTA
We are working towards imaging the surfaces and circumstellar envelopes of Mira stars in the near-infrared, using the IOTA interferometer and the IONIC integrated-optics 3-beam combiner. In order to study atmospheric structures of these stars, we installed 3 narrow-band filters that subdivide H-band into 3 roughly equal-width sub-bands - a central one for continuum, and 2 adjacent ones to sample Mira star's (mostly water) absorption-bands. We present here our characterization of the IOTA 3-Telescope interferometer for closure-phase measurements with broad and narrow-band filters in the H atmospheric window. This includes characterizing the stability, chromaticity, and polarization effects of the present IOTA optics with the IONIC beam-combiner, and characterizing the accuracy of our closure phase measurements
The fiber coupler and beam stabilization system of the GRAVITY interferometer
We present the installed and fully operational beam stabilization and fiber
injection subsystem feeding the 2nd generation VLTI instrument GRAVITY. The
interferometer GRAVITY requires an unprecedented stability of the VLTI optical
train to achieve micro-arcsecond astrometry. For this purpose, GRAVITY contains
four fiber coupler units, one per telescope. Each unit is equipped with
actuators to stabilize the telescope beam in terms of tilt and lateral pupil
displacement, to rotate the field, to adjust the polarization and to compensate
atmospheric piston. A special roof-prism offers the possibility of on-axis as
well as off-axis fringe tracking without changing the optical train. We
describe the assembly, integration and alignment and the resulting optical
quality and performance of the individual units. Finally, we present the
closed-loop performance of the tip-tilt and pupil tracking achieved with the
final systems in the lab.Comment: 14 pages, 13 figures. Proceedings of the SPIE 9146 "Optical and
Infrared Interferometry IV
Characterizing closure-phase measurements at IOTA
We are working towards imaging the surfaces and circumstellar envelopes of Mira stars in the near-infrared, using the IOTA interferometer and the IONIC integrated-optics 3-beam combiner. In order to study atmospheric structures of these stars, we installed 3 narrow-band filters that subdivide H-band into 3 roughly equal-width sub-bands - a central one for continuum, and 2 adjacent ones to sample Mira star's (mostly water) absorption-bands. We present here our characterization of the IOTA 3-Telescope interferometer for closure-phase measurements with broad and narrow-band filters in the H atmospheric window. This includes characterizing the stability, chromaticity, and polarization effects of the present IOTA optics with the IONIC beam-combiner, and characterizing the accuracy of our closure phase measurements
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